Section 2 — Recombination 



replication, or wncther it occurs only subsequent 

 to the treatment. 



2.15. Centromeres and Sites of Affinity Located on 

 Saccharomyces Chromosomes. Carl C. Lin- 



DEGREN, YUH LlN HWANG, J. K. BHATTACHAR- 



jee and Gertrude Lindegren (Carbondale, 

 U.S.A.). 



The analysis of data from more than 5000 

 yeast tetrads has revealed eleven independently 

 segregating centromeres and five sites of affinity, 

 confirming the data previously reported by 

 Lindegren et al. (1962) concerning Chromo- 

 somes I to X. The centromeres (C), their markers 

 and the number of linked genes, in parentheses, 

 are: 



Ci, ad-1 (1); Cn, ga-1 (8); Cm, le-2 (5); 

 Civ, tr-1 (1); Cv, ur-3 (14); 



Cvi, hi-2 (4); Cvn, le-1 (3); Cvm, ar-4 (1); 

 Cix, hi-6(2);C x , met-3 (1). 



The new eleventh centromere-marker, met- 14, 

 is about 10 strains from Centromere XI. A 

 cluster of 4 sites of affinity linked to 6 genes lies 

 near Centromere V; a fifth, linked to 2 genes, 

 lies near Centromere VIII. Four segments 

 containing 11 genes are not yet linked to cen- 

 tromeres. The homogeneity of data between 

 crosses has been examined and gene-to-centro- 

 mere distances have been calculated to a high 

 order of accuracy. 



2.16. Comparison of Sexual Recombination in Escheri- 

 chia coli with Gene Recombination in Strep- 

 tomyces violaceoruber. S. G. Bradley (Min- 

 neapolis, U.S.A.). 



E. coli cells and S. violaceoruber hyphae 

 contain several to many sets of genetic informa- 

 tion. In neither organism is the germ plasm 

 separated from the cytoplasm by a well-defined 

 nuclear membrane. Cellular or hyphal fusion 

 therefore is tantamount to nuclear fusion. The 

 resulting heterogenomic state is maintained 

 during several cell divisions in E. coli and indefi- 

 nitely in the mycelia of S. violaceoruber. 

 Homogenomy is established in S. violaceoruber 

 by serial plating of spores. In both microbes, 

 parental types are recovered frequently from 

 recombinant clones. Many recombinant pheno- 

 types may be derived from a single heterogeno- 

 mic clone. Different sublines of a heterogenomic 

 clone often show disparate patterns of segrega- 

 tion for one or more characters. Recombinant 

 clones may appear homogeneous for some ex- 



pressions but heterogeneous for others. These 

 results are best explained in terms of repeated 

 opportunity for recombination during vegetative 

 growth. The recombinational process in both 

 microbes is essentially similar to parasexuality 

 as described in Aspergillus by Pontecorvo. S. 

 violaceoruber differs from E. coli in that the 

 mycelial growth habit of the former stabilizes 

 the heterogenomic state whereas the relatively 

 regular cell division of the latter establishes 

 homogeneity rather quickly. If pedigrees based 

 on single cells and serial spore analyses are 

 compared, this difference disappears. Another 

 difference is that S. violaceoruber seems to 

 possess two linkage groups capable of indepen- 

 dent segregation whereas E. coli has a single 

 linkage group. 



2.17. Mitotic Recombination within the pabal Re- 

 gion of Aspergillus nidulans. Alexandra 

 Putrament (Warsaw, Poland). 



The results of analysis of 393 mitotic recom- 

 binants within the pabal region of Aspergillus 

 nidulans can be summarized as follows: 



Chromatid segregation following intragenic 

 mitotic recombination is not random. Wild- 

 type (selected) strands segregate preferentially 

 with non-recombinant ones. 



Reciprocal, non-reciprocal and probably 

 inexactly reciprocal exchanges can occur in 

 intragenic mitotic recombination. 



In intragenic mitotic recombination within 

 one effective pairing segment exchanges can 

 occur between three or even four chromatids. 



Negative interference observed in intragenic 

 mitotic recombination in Aspergillus nidulans 

 is higher than that observed in meiotic recombi- 

 nation within the same gene (pabal). In fact 

 it resembles rather the pattern of intragenic 

 meiotic recombination observed in Neurospora 

 crassa. 



Polarity of recombination observed in the 

 present work has the same tendency as that ob- 

 served in meiotic recombination within the 

 pabal region; it is even more pronounced. 



2.18. Mitotic Recombination in Translocation Hetero- 

 zygotes of Aspergillus nidulans. Etta Kafer 

 (Montreal, Canada). 



A variety of rare segregants can be isolated 

 from vegetative diploid cells of the normally 

 haploid fungus A. nidulans. These segregants 

 are of a few specific types and most of them 



14 



